This invention concerns an automatic shut-off valve for a wet barrel hydrant and is particularly directed to a valve structure which, when the hydrant is destroyed or disabled, closes off the uncontrolled flow of water therefrom in a manner which minimizes water hammer in the system lines.
In mild climates where ground freezing temperatures are rare and of short duration, the underground fire protection system of a municipality may employ fire hydrants having a manual shut-off valve located above ground. In this situation the hydrant itself holds water at the system pressure which may be in the range of 50 to 150 pounds per square inch. These hydrants are called wet barrel hydrants because a full head of water is always contained within them.
On occasion fire hydrants are damaged from impact by motor vehicles and frequently hydrants are sheared completely off the hydrant riser. To contain the resulting geyser as well as to conserve water in the system, automatic shut-off valves are provided in wet barrel hydrants and these have been constructed along the principles taught in the Greenberg Pat. No. 2,054,561, issued Sept. 15, 1936. There a breakable rod is recessed into the inside wall of the hydrant structure to hold in the non-operative position a flapper type check valve under spring bias. Should the hydrant be sheared from its support, the rod breaks to release the flapper type check valve which is urged by the spring into the out rushing water path and thus will slam the flapper against the valve seat very rapidly to halt the water flow. The abrupt closing of the automatic shut-off valve produces an enormous water hammer in the system and is known to have caused breakage in smaller lines connected in the system.
An important object of this invention is to provide an automatic hydrant shut-off valve structure which closes relatively slowly and serves to reduce almost entirely water hammer in the system.
Another object of the invention is to provide a hydrant shut-off valve of the type described which is mounted to the associated hydrant with a pressure proof but weakened connection providing a plane of preferential sheering when the hydrant receives destructive lateral impact.
Another object of the invention is to provide a hydrant shut-off valve of the type described which includes provisions for a "witness stream" visible to passers-by to signify the damaged fire hydrant.
Another object of the invention is to provide a "wet" hydrant shut-off or check valve of the type described which is readily installed and placed in operative condition both for new system installations and as a replacement in existing fire protection systems.
Another object of the invention is to provide a hydrant automatic check valve and connection assembly which breaks-away upon high impact and thereby reduces damage to the hydrant body.